Methods for treating hypertension, and angina using optically pure (-) amlodipine

ABSTRACT

Methods are disclosed utilizing the optically pure (-) isomer of amlodipine. This compound is a potent drug for the treatment of hypertension while avoiding the concomitant liability of adverse effects associated with the racemic mixture of amlodipine. The (-) isomer of amlodipine is also useful for the treatment of angina without the concomitant liability of adverse effects associated with the racemic mixture of amlodipine.

This is a continuation of application Ser. No. 07/981,562 filed Nov. 25,1992, now abandoned, which is a continuation-in-part of application Ser.No. 07/798,466 filed Nov. 26, 1991, now abandoned, each of which isincorporated by reference herein in its entirety.

BACKGROUND OF THE INVENTION

This invention relates to novel compositions of matter containingoptically pure (-) amlodipine. These compositions possess potentactivity in treating both systolic and diastolic hypertension whileavoiding adverse effects including but not limited to edema of theextremities, headache and dizziness, which are associated withadministration of the racemic mixture of amlodipine. Additionally, thesenovel compositions of matter containing optically pure (-) amlodipineare useful in treating angina and such other conditions as may berelated to the activity of (-) amlodipine as a calcium channelantagonist including but not limited to cerebral ischemia, cerebraldisorders, arrhythmias, cardiac hypertrophy, coronary vasospasm,myocardial infarction, renal impairment and acute renal failure--whileavoiding the adverse effects associated with administration of theracemic mixture of amlodipine. Also disclosed are methods for treatingthe above-described conditions in a human while avoiding the adverseeffects that are associated with the racemic mixture of amlodipine, byadministering the (-) isomer of amlodipine to said human.

Steric Relationship and Drug Action

Many organic compounds exist in optically active forms, i.e., they havethe ability to rotate the plane of plane-polarized light. In describingan optically active compound, the prefixes D and L or R and S are usedto denote the absolute configuration of the molecule about its chiralcenter(s). The prefixes d and l or (+) and (-) are employed to designatethe sign of rotation of plane-polarized light by the compound, with (-)or 1 meaning that the compound is levorotatory. A compound prefixed with(+) or d is dextrorotatory. For a given chemical structure, thesecompounds, called stereoisomers, are identical except that they aremirror images of one another. A specific stereoisomer may also bereferred to as an enantiomer, and a mixture of such isomers is oftencalled an enantiomeric or racemic mixture.

Stereochemical purity is of importance in the field of pharmaceuticals,where 12 of the 20 most prescribed drugs exhibit chirality. A case inpoint is provided by the L-form of the β-adrenergic blocking agent,propranolol, which is known to be 100 times more potent than theD-enantiomer.

Furthermore, optical purity is important since certain isomers mayactually be deleterious rather than simply inert. For example, it hasbeen suggested that the D-enantiomer of thalidomide was a safe andeffective sedative when prescribed for the control of morning sicknessduring pregnancy, while the corresponding L-enantiomer has been thoughtto be a potent teratogen.

The active compound of this composition and method is an optical isomerof the compound amlodipine, which is described in Davison et al., U.S.Pat. No. 4,572,909. Chemically, this (-) isomer is 3-ethyl5-methyl(-)-2-[(2-aminoethoxy)methyl]-4-(2-chlorophenyl)-1,4-dihydro-6-methyl-3,5-pyridine-dicarboxylate.This isomer will hereinafter be referred to as (-) amlodipine. (-)Amlodipine also includes the substantially optically pure (-) amlodipineisomer.

Amlodipine, which is the subject of the present invention, is availablecommercially only as the 1:1 racemic mixture. That is, it is availableonly as the 1:1 mixture of optical isomers, called enantiomers. Theracemic mixture of amlodipine that is commercially available foradministration is a besylate salt.

Pharmacologic Action

The racemic mixture of amlodipine is in the class of compounds known ascalcium antagonists. The concept of a specific mechanism ofpharmacologic action related to the antagonism of calcium movement inthe process of excitation-contraction was suggested by Fleckenstein et.al. (see Fleckenstein, A., Calcium Antagonism in Heart and SmoothMuscle: Experimental Facts and Therapeutic Prospects, New York, Wiley,1983; Swamy, V. and D. Triggle, Modern Pharmacology, 2nd. Ed., Craig andStitzel, Eds., Little, Brown and Co., Boston, 1986, Chapt. 26, 373-380;Triggle, D. J., and R. A. Janis, Ann. Rev. Pharm. and Tox. 27: 347-369,1987). Many of the currently available calcium antagonists appear toantagonize the entry of calcium through voltage dependent channels inthe plasma membrane of cells. The pharmacologic class of calciumantagonists consists of chemically diverse compounds. Given thestructural heterogeneity of the class it is likely that thepharmacological action involves more than one site or mechanism ofaction.

Amlodipine is one of a series of dihydropyridine calcium antagonists.However, amlodipine has a generally slower onset and longer duration ofaction than, for example, nifedipine. (Jensen, H. et al., J. Hum.Hypertens., 42(5): 541-45, 1990). The metabolites of amlodipineapparently do not possess significant calcium channel blocking activity,while the parent drug offers a biological half-life of some 35-40 hours,prompting a once-daily dosage regimen. (Lorimer, A. R., et al., J. Hum.Hypertens., 3(3): 191-96, 1989; Glasser, S. F. et al., AJH, 2(3):154-57, 1989). Its ability to block calcium channels in smooth muscleproduces peripheral vasodilation resulting in decreases in both systolicand diastolic blood pressure.

With regard to the enantiomers of amlodipine, these are disclosed inArrowsmith et al. J. Med. Chem., 29: 1696-1702 (1986). This referencediscusses in vitro tests to determine calcium antagonist activityagainst calcium-induced constriction of potassium-depolarized rat aorta.The authors allege that in vitro evaluation of the enantiomers ofamlodipine shows the (-) isomer to be twice as active as the racemicmixture in antagonizing calcium-induced constriction ofpotassium-depolarized rat aorta. The authors also allege that the (+)isomer of amlodipine is some 1,000 times less active in these in vitrotests. Further, European Patent Application No. 0 331 315 discloses amethod for separation of the R(-) and S(+) isomers of amlodipine. Whilethese references discuss the enantiomers of amlodipine, they onlyprovide a method of synthesis and in vitro test results of theindividual enantiomer activity as found in rat aorta. There is nodisclosure of the effects of or a suggestion for administering one ofthe enantiomers of amlodipine to a human. Moreover, there is nodisclosure or suggestion of the alleviation or reduction of side effectswhich is achieved by the administration of (-) amlodipine.

The racemic mixture of amlodipine is presently used primarily as anantihypertensive agent; it is generally taken orally as a once-dailytherapy. As stated above, the racemic mixture of amlodipine producesperipheral vasodilation, resulting in decreases in both systolic anddiastolic blood pressure when used as an antihypertensive agent. Thisantihypertensive effect occurs in the relative absence of significant orsustained effects on cardiac rate.

While yet the subject of extensive research, hypertension appears to bethe product of an inherited predisposition--coupled with dietary,emotional, and environmental factors, which results in a structuraladaptation of the cardiac muscle and the large blood vessels. Mostpatients display heightened vascular and cardiac reactions tosympathetic nervous stimulation, but the precise relationship ofsympathetic nervous stimulation to the etiology of the disease.Nevertheless, hypertension results in chronic readjustment ofcardiovascular hemodynamics, alteration of blood vessel walls,cardiovascular resistance and regional transmural pressures.

Pharmacologic management of hypertension is generally directed to thenormalization of altered hemodynamic parameters, and many drugs and drugclasses, either as monotherapy or in combination treatment, can reduceand control elevated blood pressure. However, treatment of hypertensiondoes not always correspondingly benefit the morbidity and mortality ofthe condition, either because chronic hypertension has produced othersignificant and irreversible cardiovascular changes, or because presentdrugs have an adverse effect on some other risk factor forcardiovascular disease. Rather, current drug therapy simply providessustained arterial pressure reduction.

Furthermore, the racemic mixture of amlodipine is useful in treatingother disorders such as angina pectoris.

Angina pectoris is a highly variable, rather poorly understood clinicalsyndrome reflecting a myocardial ischemia. When cardiac work ormyocardial oxygen demand exceeds the ability of the coronary arterialvascular system to supply oxygen, the resulting ischemia stimulates thesensory nerves of the heart, producing the sensation of anginacharacterized by episodes of precordial pressure, discomfort, or asevere, intense crushing pain which may radiate to several sitesincluding the left shoulder and left arm. Physical activity or exertioncharacteristically initiates the condition, and rest or drug therapyrelieves the condition. The signs and symptoms of an episode persist fora few minutes, but can be induced or exaggerated by a meal or exposureto cold air. Treatment is directed to the underlying disease, usuallyatherosclerosis, or to drugs which either reduce myocardial oxygendemand or improve oxygen supply. Calcium antagonists such as amlodipinehave been particularly useful in treating vasospastic angina, the anginaof effort, and the unstable angina, due to the effect of the calciumchannel antagonist on cardiac and vascular smooth muscle.

Amlodipine may be useful in the treatment of cerebral ischemia. Cerebralischemia, often the result of atherosclerotic disease or hypertension,results from insufficient cerebral circulation. Under normalcircumstances, an extensive collateral circulation ensures adequateblood flow. However, cerebral ischemia may result from either an intra-or extracranial interruption of arterial blood flow. If interruption istransient, the cerebral tissues recover, and neurologic symptomsdisappear. If the ischemia lasts for a somewhat more extended period,infarction results and the resulting neurologic damage is permanent. Inthe case of extended ischemia resulting in infarction, treatment isdirected to the underlying vascular disease, to blood plateletaggregation inhibitors, and anticoagulant therapy.

Because of its activity as a calcium channel antagonist, amlodipine mayalso be useful in treating cardiac arrhythmias. Cardiac arrhythmiasrepresent a broad, complex group of electrophysiologic disorders thataffect the mechanical properties of the heart and vasculature, alteringnormal cardiac rhythm, function and output. Normal cardiac rhythmoriginates with the sinoatrial node, which possesses high intrinsicautomaticity. Adequate automaticity and conduction lead to activation ofatrial and ventricular fibers, producing in sequence the elements ofnormal functional heart beat. Calcium antagonists may be of value inconditions where calcium-related changes in membrane potential andconduction alter normal rhythm. In the absence of treatment, symptomsvary with individual arrhythmias, but are often the consequence ofinadequate cardiac filling and output and often include fatigue,decreased exercise tolerance, syncope, shortness of breath, nausea,lightheadedness and the like.

Amlodipine may be useful to treat cardiac hypertrophy. Cardiachypertrophy can result from excessive workload either due to anobstruction to outflow, termed systolic overload, or to excessivevolumes presented to the heart in diastole, termed diastolic overload.Systolic overload results in concentric ventricular hypertrophy, inwhich there is an increased thickness in the walls of the heart notassociated with increased volume. Diastolic overload causes dilation andhypertrophy with an increased blood volume. An inadequate cardiac outputresults from the heart's failure in systolic or diastolic overload,leading to fatigue, shortness of breath, pulmonary congestion, edema andthe like. Calcium channel antagonists effect workload and, as such, maybe useful in treating cardiac hypertrophy due to the effect of thecalcium antagonist on cardiac and vascular smooth muscle in reducingblood pressure.

It is also possible that amlodipine could be used to treat coronaryarterial spasm. Coronary arterial spasm can occur in the absence ofsignificant coronary atherosclerosis and is thought to be an initiatingevent in variant angina and in myocardial infarction. Coronary spasm mayoccur without the patient feeling any significant discomfort. In anelectrically unstable heart, diverse neural impulses to the heart mayprovoke coronary vascular spasm. This may result in enhanced myocardialischemia and arrhythmia, which in turn may culminate in ventricularfibrillation and sudden cardiac death. As in variant or vasospasticangina, the calcium channel antagonists may be of particular usefulnessdue to their effect on cardiac and vascular smooth muscle.

Furthermore, amlodipine may be useful in the treatment of myocardialinfarction, ischemic myocardial necrosis, and ischemia reperfusioninjury. Myocardial infarction or ischemic myocardial necrosis generallyresults from the abrupt reduction of coronary blood flow to a portion ofthe myocardium. The condition likely originates from atherosclerosis ofthe coronary arteries. Either coronary artery vasospasm or acutecoronary thrombosis precipitates the condition, although the etiology isthe subject of continuing research. Myocardial infarction ispredominantly a disease of the left ventricle. Precordial pain and leftventricular dysfunction characterize the disease. The pain, which can besevere aching or pressure, leads to apprehension. Symptoms include leftventricular heart failure, pulmonary edema, shock or significant cardiacarrhythmia. Calcium channel antagonists may find utility in themanagement of myocardial infarction patients due to their effects oncoronary artery vasospasm, blood pressure or other effects on cardiacfunction or vascular smooth muscle.

Amlodipine may be used to treat congestive heart failure. Congestiveheart failure can be caused by hypertension, cardiomyopathy, coronaryartery disease or valvular heart disease. Congestive failure results inpoor cardiac output and elevated left-ventricular diastolic pressure,leading to dyspnea, fatigue, peripheral edema, and coughing. The abilityof some calcium antagonists to lower afterload by dilating peripheralarteries without having a significant inotropic effect may increasetheir use in treating congestive heart failure.

Amlodipine may be of use in treating migraine. Classic migrainetypically begins with visual auras followed by severe headaches, oftenaccompanied by nausea and vomiting. Common migraine has similar symptomswithout the preceding visual aura. The causes of migraine have beenstudied intensely, and are still a matter of debate. The most generallyaccepted cause is hypoxia due to reduced cerebral blood flow. Calciumchannel antagonists have been used for migraine prophylaxis since theycan increase cerebral blood flow.

Amlodipine may also be useful for treating Raynaud's phenomenon, whichis characterized by vascular spasm of the extremities. These vasospasmscan be caused by cold or stress. A pallor or cyanosis is usually presentdue to severe constriction of the digital arteries. The phenomenon isoften seen as a secondary disorder with arterial diseases or connectivetissue diseases such as scleroderma, arthritis or lupus erythematosus.Calcium channel antagonists have been shown to be effective in treatingRaynaud's phenomenon.

Amlodipine may be useful in the treatment of asthma and bronchospasm.Symptoms of asthma--coughing, wheezing, and dyspnea--are caused byconstriction of tracheobronchial smooth muscle. Asthma attacks can betriggered by antigenic stimuli (pollen, dust) or non-antigenic stimuli(exercise, pollution, infection). The response to these stimuli lead tosecretions of chemical mediators that cause smooth muscle contraction.Calcium channel antagonists can be used to control bronchoconstrictionand relieve asthma attacks.

In addition, the racemic mixture of amlodipine may be useful to treatrenal impairment and acute renal failure. Renal impairment and acuterenal failure are clinical conditions of diverse etiology, which areassociated with an increasing azotemia or urea nitrogen in the blood,and often an oliguria or a diminished volume of urine in relation tofluid intake. The pathophysiology may originate prerenally, manifest asinadequate renal perfusion, due to extracellular fluid volume depletionor cardiac failure. The most common cause of intrinsic renal failure isprolonged renal ischemia. Postrenal azotemia may be associated withobstruction or renal glomerular and tubular dysfunction. Laboratoryfindings disclose progressive azotemia, acidosis, hyperkalemia, andhyponatremia. Factors aggravating kidney impairment or failure must bespecifically treated, including heart failure, obstruction and the like.Moderate or severe hypertension has a deleterious effect on renalfunction, and management of the hypertension with a variety of drugsincluding calcium channel antagonists may be useful therapy.

In addition, the racemic mixture of amlodipine could be useful in thetreatment of cognitive disorders. Cognitive disorders include but arenot limited to dementia and age-associated memory impairment.

Dementia can occur at any age. It is a structurally caused permanent orprogressive decline in several dimensions of intellectual function thatinterferes substantially with individual normal social or economicactivity.

One particular type of dementia is Alzheimers-type dementia.Alzheimers-type of dementia is thought to be due to a degenerativeprocess, with a large loss of cells from the cerebral cortex and otherbrain areas. Acetylcholine-transmitting neurons and their target nervecells are particularly affected. The brain shows marked atrophy withwide sulci and dilated ventricles. Senile plaques and neurofibrillarytangles are present. Memory loss is the most prominent early symptom.Disturbances of arousal do not occur early in the course. Alzheimer'spresenile and senile onset dementias are similar in both clinical andpathologic features, with the former commonly beginning in the 5th and6th decades and the latter in the 7th and 8th decades. The dementiausually progresses steadily, becoming well advanced in 2 to 3 years.Some cases of dementia occurring in the presenile period are hard toclassify and are sometimes labelled idiopathic or simple preseniledementia.

The signs and symptoms of dementia in particular Alzheimers-typedementia include depression, paranoia, anxiety or any of several otherpsychologic symptoms. The most common clinical picture is slowdisintegration of personality and intellect due to impaired insight andjudgment and loss of affect. Memory impairment increases, beginning withproblems recalling recent events or finding names. The impairment variesgreatly from time to time and often from moment to moment. Dementiagenerally is an insidious, slowly progressive, untreatable condition.However, the rate of progression varies widely and depends on the cause.

Another type of cognitive disorder is age-associated memory impairment(AAMI). AAMI is used to describe healthy non-demented people who haveexperienced memory loss over the course of the person's life. Mostcommonly it is used to describe adults over the age of 50 who haveexperienced memory loss over the course of adult life. It has beenestimated that between 25% and 50% of people over the age of 65 havethis disorder.

Many calcium channel antagonists cause significant adverse effects.These adverse effects include but are not limited to tachycardia,orthostatic hypotension and fluid retention. In contrast to thesituation with several other calcium channel antagonists, however, theracemic mixture of amlodipine has not been found to cause either markedor prolonged direct effects on heart rate or the reflex consequence ofvasodilation.

However, the administration of the racemic mixture of amlodipine to ahuman has been found to cause still other adverse effects. These adverseeffects include but are not limited to edema of the extremitiesincluding peripheral edema, headache, flushing/hot flashes, fatigue,vertigo, muscle cramps and dizziness.

Thus, it would be particularly desirable to find a compound with theadvantages of the racemic mixture of amlodipine which would not have theaforementioned disadvantages of significant adverse side effects andwhich was useful for treatment of other conditions.

SUMMARY OF THE INVENTION

It has now been discovered that the optically pure (-) isomer ofamlodipine is an effective antihypertensive agent for both systolic anddiastolic hypertension, particularly in mild to moderate disease andangina, while avoiding adverse effects including but not limited toedema of the extremities, headache and dizziness, which are associatedwith the administration of the racemic mixture of amlodipine. It hasalso been discovered that these novel compositions of matter containingoptically pure (-) amlodipine are useful in treating other conditions asmay be related to the activity of (-) amlodipine as a calcium channelantagonist, including but not limited to cerebral ischemia, cerebraldisorders, arrhythmias, cardiac hypertrophy, coronary vasospasm,myocardial infarction, renal impairment and acute renal failure whileavoiding the above-described adverse effects associated with theadministration of the racemic mixture of amlodipine. The presentinvention also includes methods for treating the above-describedconditions in a human while avoiding the adverse effects that areassociated with the racemic mixture of amlodipine by administering the(-) isomer of amlodipine to said human.

DETAILED DESCRIPTION OF THE INVENTION

The present invention encompasses a method of eliciting anantihypertensive effect in a human, while avoiding the concomitantliability of adverse effects, which comprises administering to saidhuman in need of such antihypertensive therapy, an amount of (-)amlodipine or a pharmaceutically acceptable salt thereof, substantiallyfree of its (+) stereoisomer, said amount being sufficient to alleviatehypertension, but insufficient to cause said adverse effects associatedwith administration of racemic amlodipine.

The present invention also encompasses an antihypertensive compositionfor the treatment of a human in need of antihypertensive therapy, whichcomprises an amount of (-) amlodipine or a pharmaceutically acceptablesalt thereof, substantially free of its (+) stereoisomer, said amountbeing sufficient to alleviate said hypertension but insufficient tocause adverse effects of racemic amlodipine.

The present invention further encompasses a method of treating angina ina human, while avoiding the concomitant liability of adverse effects,which comprises administering to said human in need of such anti-anginatherapy, an amount of (-) amlodipine, or a pharmaceutically acceptablesalt thereof, substantially free of its (+) stereoisomer, said amountbeing sufficient to alleviate said condition but insufficient to causesaid adverse effects associated with administration of racemicamlodipine.

In addition, the present invention encompasses an antianginalcomposition for the treatment of a human having angina, which comprisesan amount of (-) amlodipine or a pharmaceutically acceptable saltthereof, substantially free of its (+) stereoisomer, said amount beingsufficient to alleviate said angina but insufficient to cause adverseeffects of racemic amlodipine.

A further aspect of the present invention includes a method of treatinga condition caused by excessive calcium influx in cells in a human,while avoiding the concomitant liability of adverse effects, whichcomprises administering to said human in need of a reduction inexcessive calcium influx an amount of (-) amlodipine, or apharmaceutically acceptable salt thereof, substantially free of its (+)stereoisomer, sufficient to alleviate said condition but insufficient tocause said adverse effects of racemic amlodipine. Conditions caused byexcessive calcium influx in cells in a human include but are not limitedto cerebral ischemia, cerebral disorders such as cognitive disordersincluding but not limited to Alzheimer's dementia and memory impairment,arrhythmias, cardiac hypertrophy, congestive heart failure, coronaryvasospasm, migraine, bronchospasm and asthma, Raynaud's phenomenon,myocardial infarction, renal impairment and acute renal failure.

Furthermore, the present invention includes a composition for treating acondition caused by excessive calcium influx in cells in a human, whichcomprises an amount of (-) amlodipine, or a pharmaceutically acceptablesalt thereof, substantially free of its (+) stereoisomer, said amountbeing sufficient to alleviate said condition but insufficient to causeadverse effects of racemic amlodipine.

The commercially available racemic mixture of amlodipine (e.g., a 1:1racemic mixture of the two enantiomers) causes antihypertensive andantianginal activity; however, this racemic mixture, while offering theexpectation of efficacy, causes adverse effects. Utilizing the (-)isomer of amlodipine results in clearer dose-related definitions ofefficacy, surprisingly diminished adverse effects, and accordingly, animproved therapeutic index. It is, therefore, more desirable to use the(-) isomer of amlodipine.

The term "adverse effects" includes, but is not limited to,cardiovascular effects (including tachycardia and diminishedcontractility of the heart), edema of the extremities, headache,dizziness, flushing, fatigue, vertigo, and muscle cramps.

The term "substantially free of its (+) stereoisomer" as used hereinmeans that the composition contains a greater proportion or percentageof the (-) isomer of amlodipine in relation to the (+) isomer ofamlodipine, said percentage being based on the total amount ofamlodipine. In a preferred embodiment the term "substantially free ofits (+) stereoisomer means that the composition contains at least 90% byweight of (-) amlodipine, and 10% by weight or less of (+) amlodipine.In the most preferred embodiment the term "substantially free of the (+)stereoisomer" means that the composition contains at least 99% by weight(-) amlodipine, and 1% or less of (+) amlodipine. In another preferredembodiment the term "substantially free of its (+) stereoisomer" as usedherein means that the composition contains 100% by weight of (-)amlodipine. The terms "substantially optically pure (-) isomer ofamlodipine" and "optically pure (-) isomer of amlodipine are alsoencompassed by the above-described meanings.

The term "eliciting an antihypertensive effect" as used herein meansproviding a normalization to otherwise elevated systolic and/ordiastolic blood pressure, and by so doing providing relief from anypossible symptoms or other hemodynamic effects caused by the elevatedpressure.

The term "a method of treating angina" as used herein means relief fromthe symptoms of myocardial ischemia, which include, but are not limitedto, episodes of precordial pressure, discomfort, or a severe intense,crushing pain which may radiate, and which may be accompanied by changesin respiration, pulse rate, and blood pressure.

The term, "a condition caused by excessive calcium influx in cells in ahuman" includes but is not limited to conditions involving calciuminflux in human cell that may be present in smooth muscle, cardiac, andother tissues including lung and brain. These conditions include, butare not limited to, cerebral ischemia, cerebral disorders such ascognitive disorders including Alzheimer's dementia and memoryimpairment, arrhythmias, cardiac hypertrophy, congestive heart failure,coronary vasospasm, migraine, bronchospasm and asthma, Raynaud'sphenomenon, myocardial infarction, renal impairment and acute renalfailure. The symptoms associated with these disorders include, but arenot limited to, the symptoms of precordial discomfort or pain, headache,fatigue, decreased exercise tolerance, syncope, shortness of breath,nausea, lightheadedness, edema, pulmonary congestion, arrhythmia orpalpitation, azotemia, and/or oliguria.

The chemical synthesis of the racemic mixture of amlodipine can beperformed by the method described in Arrowsmith, J. E. et al., J. Med.Chem., 29: 1696-1702 (1986).

A technique for separation of the (-) amlodipine isomer from the racemicmixture is illustrated schematically (see Arrowsmith, J. E., EP 331,315)as follows: ##STR1##

The racemic acid 1 is converted to its cinchonidine salts in methanolsolution. Upon dilution with water and standing at room temperature, acrystalline precipitate is formed which can be subsequentlyrecrystallized to constant rotation to give the diastereomerically purecinchonidine salt 2. Further, the mother liquids from the originalcrystallization can be reduced in volume and stirred at roomtemperature, e.g. overnight, to afford a fine precipitate which can alsobe recrystallized to give the diastereomerically pure cinchonidine salt2. The cinchonidine salt 2 is partitioned between ethyl acetate anddilute hydrochloric acid to liberate the (+) acid 3. The acid 3 is thenesterified using carbonyldimidazole (CDI) in near-quantitative yield byforming an imidazolide and decomposing the imidazolide with ethanolicsodium ethoxide to give 4. The azido group in 4 can then be cleanlyreduced to amino by catalytic hydrogenation, giving (-) amlodipine,which is most conveniently isolated as the salt of an acid, e.g. as themaleate 5.

The magnitude of a prophylactic or therapeutic dose of (-) amlodipine inthe acute or chronic management of disease will vary with the severityof the condition to be treated and the route of administration. Thedose, and perhaps the dose frequency, will also vary according to theage, body weight, and response of the individual patient. In general,the total daily dose ranges, for the conditions described herein, isfrom about 0.01 mg. to about 100.0 mg. Preferably, a daily dose rangeshould be between about 0.5 mg to about 20.0 mg. while most preferably,a daily dose range should be between about 0.5 mg to about 10 mg. Inmanaging the patient, the therapy should be initiated at a lower dose,perhaps about 0.025 mg to about 2.5 mg and increased up to about 20 mgor higher depending on the patient's global response. It is furtherrecommended that children and patients over 65 years, and those withimpaired renal or hepatic function, initially receive low doses, andthat they be titrated based on global response and blood level. It maybe necessary to use dosages outside these ranges in some cases.

The various terms, "an amount sufficient to alleviate hypertension butinsufficient to cause said adverse effects, "an amount sufficient toalleviate said condition but insufficient to cause said adverse effects"wherein said condition is angina; and "an amount sufficient to alleviatesaid condition but insufficient to cause said adverse effects" whereinsaid condition includes but is not limited to cerebral ischemia,cerebral disorders, arrhythmias, cardiac hypertrophy, coronaryvasospasm, myocardial infarction, renal impairment and acute renalfailure are encompassed by the above described dosage amounts and dosefrequency schedule.

Any suitable route of administration may be employed for providing thepatient with an effective dosage of (-) amlodipine. For example, oral,rectal, parenteral, transdermal, subcutaneous, intramuscular, and thelike may be employed. Dosage forms include tablets, troches,dispersions, suspensions, solutions, capsules, patches, and the like.

The pharmaceutical compositions of the present invention comprise (-)amlodipine as active ingredient, or a pharmaceutically acceptable saltthereof, and may also contain a pharmaceutically acceptable carrier, andoptionally, other therapeutic ingredients.

The term "pharmaceutically acceptable salts" refers to salts preparedfrom pharmaceutically acceptable non-toxic acids including inorganicacids and organic acids.

Since the compound of the present invention is basic, salts may beprepared from pharmaceutically acceptable non-toxic acids includinginorganic and organic acids. Such acids include acetic, benzene-sulfonic(besylate), benzoic, camphorsulfonic, citric, ethenesulfonic, fumaric,gluconic, glutamic, hydrobromic, hydrochloric, isethionic, lactic,maleic, malic, mandelic, methanesulfonic, mucic, nitric, pamoic,pantothenic, phosphoric, succinic, sulfuric, tartaric acid,p-toluenesulfonic, and the like. Particularly preferred are besylate,hydrobromic, hydrochloric, phosphoric and sulfuric acids. (See Campbell,S. F. et al., U.S. Pat. No. 4,806,557.)

The compositions include compositions suitable for oral, rectal andparenteral (including subcutaneous, intramuscular, and intravenous)administration, although the most suitable route in any given case willdepend on the nature and severity of the condition being treated. Themost preferred route of the present invention is the oral route. Thecompositions may be conveniently presented in unit dosage form, andprepared by any of the methods well known in the art of pharmacy.

In the case where an oral composition is employed, a suitable dosagerange for use is from about 0.01 mg. to about 100.0 mg. total dailydose, given as a once daily administration in the morning or in divideddoses if required. Preferably, a dose range of between about 0.5 mg toabout 20.0 mg is given as a once daily administration or in divideddoses if required, and most preferably a dose range of from betweenabout 0.5 mg to about 10.0 mg is given as a once daily administration orin divided doses if required. Patients may be upward titrated from belowto within this dose range to a satisfactory control of symptoms or bloodpressure as appropriate.

In practical use, (-) amlodipine can be combined as the activeingredient in intimate admixture with a pharmaceutical carrier accordingto conventional pharmaceutical compounding techniques. The carrier maytake a wide variety of forms depending on the form of the preparationdesired for administration, e.g., oral or parenteral (includingintravenous injections or infusions). In preparing the compositions fororal dosage form any of the usual pharmaceutical media may be employed.Usual pharmaceutical media include, for example, water, glycols, oils,alcohols, flavoring agents, preservatives, coloring agents, and the likein the case of oral liquid preparations (such as for example,suspensions, solutions, and elixirs); aerosols; or carriers such asstarches, sugars, microcrystalline cellulose, diluents, granulatingagents, lubricants, binders, disintegrating agents and the like, in thecase of oral solid preparations (such as for example, powders, capsules,and tablets) with the oral solid preparations being preferred over theoral liquid preparations. The most preferred oral solid preparation istablets.

Because of their ease of administration, tablets and capsules representthe most advantageous oral dosage unit form, in which case solidpharmaceutical carriers are employed. If desired, tablets may be coatedby standard aqueous or nonaqueous techniques.

In addition to the common dosage forms set out above, the compounds ofthe present invention may also be administered by controlled releasemeans and/or delivery devices such as those described in U.S. Pat. Nos.:3,845,770; 3,916,899; 3,536,809; 3,598,123; and 4,008,719, thedisclosures of which are hereby incorporated by reference.

Pharmaceutical compositions of the present invention suitable for oraladministration may be presented as discrete units such as capsules,cachets, or tablets, or aerosols sprays, each containing a predeterminedamount of the active ingredient, as a powder or granules, or as asolution or a suspension in an aqueous liquid, a non-aqueous liquid, anoil-in-water emulsion, or a water-in-oil liquid emulsion. Suchcompositions may be prepared by any of the methods of pharmacy, but allmethods include the step of bringing into association the activeingredient with the carrier which constitutes one or more necessaryingredients. In general, the compositions are prepared by uniformly andintimately admixing the active ingredient with liquid carriers or finelydivided solid carriers or both, and then, if necessary, shaping theproduct into the desired presentation.

For example, a tablet may be prepared by compression or molding,optionally, with one or more accessory ingredients. Compressed tabletsmay be prepared by compressing in a suitable machine the activeingredient in a free-flowing form such as powder or granules, optionallymixed with a binder, lubricant, inert diluent, and/or surface active ordispersing agent. Molded tablets may be made by molding in a suitablemachine a mixture of the powdered compound moistened with an inertliquid diluent. Desirably, each tablet contains from about 0.01 mg toabout 50 mg of the active ingredient, and each cachet or capsulecontains from about 0.5 mg to about 50 mg of the active ingredient, (-)amlodipine. Most preferably, the tablet, cachet or capsule containseither one of three dosages, 0.5 mg, 2.5 mg and 5.0 mg (as scoredtablets, the preferable dose form) of the active ingredient.

The invention is further defined by reference to the following examplesdescribing in detail the testing and preparation of the compositions ofthe present invention. It will be apparent to those skilled in the art,that many modifications, both to materials and methods, may be practicedwithout departing from the purpose and interest of this invention.

EXAMPLES Example 1 Vascular Selectivity Studies

The relative potency of optically pure (-) amlodipine and racemicamlodipine as calcium channel antagonists and negative inotropic agentsare determined by a pharmacological study. Evaluation of these compoundsand others in in vitro test systems provide results, from which thevascular selectivity of a particular compound can be assessed. Calciumchannel antagonist activity of the compounds as a function of theirmolar concentration can be evaluated by measuring their inhibition ofthe calcium-induced contraction of strips of rat aorta immersed in abath of Krebs-Henseleit buffer containing 45 mM K+and no Ca²⁺. In thepresence of various concentrations of the antagonists, inhibition wouldoccur in the contraction of this isolated tissue preparation in responseto the addition of calcium chloride. Antagonists may be compared byexamining the molar concentration of compounds inhibiting thecalcium-induced contraction by 50%.

As an index of cardiac depression, negative inotropic activity may becomparably assessed using isolated heart preparations of adult rats. Thetissues are prepared and perfused in vitro with Krebs-Henseleit buffersolution, with the activity of the calcium channel antagonists evaluatedas a function of their concentration. The compounds are tested for theirability to alter cardiac contraction. Relative potency is calculatedfrom the IC₂₅ values of the compounds, i.e., the concentration requiredto depress contraction by 25%.

Example 2 Radioligand Binding Studies

Hind limb skeletal muscles from rats or guinea pigs are minced andhomogenized. After filtration and repeated centrifugation, the pellet ishomogenized and diluted in a Tris buffer to a protein concentration of1-3 mg/ml. Volumes of this suspension containing 3-10 μg protein areincubated in the presence of a fixed concentration of 0.2 to 0.5 nM(+)-[³ H]-isradipine or a similar radioactive ligand and increasingconcentrations of racemic amlodipine, (-) amlodipine or (+) amlodipine.After 1 hour incubation, the bound and free radioactivity is measured ina scintillation counter and the affinity of the test compounds to thereceptors is calculated.

Example 3 Effects on Coronary Vascular Resistance in the Guinea PigLangendorff Heart Preparation

Male guinea pigs weighing between 400 and 450 g are killed by cervicaldislocation. The hearts are removed and perfused with Krebs-Henseleitsolution at constant pressure (60 cm water) by means of retrogradecannulation of the aorta in a Langendorff apparatus. The Krebs-Henseleitsolution, consisting of 118.0 mM NaCl, 4.7 mM KCl, 5.5 mM CaCl₂, 1.2 mMMgSO₄, 25.0 mM NaHCO₃ and 5.0 mM glucose, is prewarmed to 37° C. andgassed with a mixture of 95% oxygen/5% carbon dioxide. A ballooncatheter connected to a pressure transducer is placed in the leftventricle via the left atrium and is preloaded to a pressure of 40 mmHg. Coronary perfusate flow is measured continuously, and changes inheart rate and left ventricular contractility are also monitoredcontinuously.

Each experiment consists of a 30 minute equilibrium period during whichcoronary flow is stabilized at 9-12 ml/min. Following this period, avasoconstrictor is injected 3 times at 40 minute intervals into thecannulated aorta. This dose of U-46619 (9,11-methanoepoxy-PGH₂) evokesapproximately a 75% decrease in coronary flow within 30-40 sec, and theeffect is fully reversible after 20-25 min continuous perfusion. Racemicamlodipine, (-) amlodipine or (+) amlodipine dissolved in dimethylsulfoxide or the vehicle are injected in increasing concentrations priorto further U-46619 injections.

The mean decrease in coronary flow obtained with three consecutiveinjections of U-46619 in the absence of the test substance is taken tobe 100% and the percent inhibition of this effect in the presence ofincreasing concentrations of the test drugs is calculated. Completeindividual dose-response curves for each test drug are generated in fivehearts, enabling the calculation of the dose for the half-maximalantivasoconstrictor effect (ID₅₀).

Example 4 Antihypertensive Efficacy in Spontaneously Hypertensive Rats

Male spontaneously hypertensive rats (300-350 g) are anesthetized, andpolyethylene catheters are implanted in the abdominal aorta via afemoral artery, and in the abdominal vena cava via a femoral vein. Thearterial catheters are connected to pressure transducers by means of anintraflow device, flushing the catheters with 3 ml/hr. Mean arterialpressures are derived electronically from the blood pressure wave. Meanpretreatment values of mean arterial pressure are in the range of160-220 mm Hg. Doses of racemic amlodipine, (-) amlodipine and (+)amlodipine, or of the solvent vehicle, are injected into the venouscatheter. Responses in mean arterial pressure to the respective drug orsolvent are registered and the relative potencies of the test compoundsare calculated.

Example 5 Cardiovascular

Calcium Antagonism, Guinea Pig Ileum (in vitro)

Test substance (3 μg/ml) inhibition of the contractile response of theK⁺ -depolarized isolated guinea pig ileal segment, bathed in Ca-freephysiological salt solution at 37° C., to added calcium (20 μg/ml ofCaCl), indicates calcium antagonist activity.

Reference Agents (ED₁₀₀, μg/ml)

    ______________________________________                                        atropine     >2        isoxuprine 4                                             cinnazrizine 1 mepyramine >5                                                  cyproheptadine 0.025 nifedipine 0.001                                         diltiazem 0.01 papaverine 4                                                   diphenhydramine 1 promethazine 0.25                                           flunarizine 0.1 propranolol 4                                                 ipratropium bromide >2 verapamil 0.01                                       ______________________________________                                    

Example 6 Studies on Insulin Resistance

Insulin is a hormone that activates various biochemical processes in thebody, the most well known being facilitation of glucose transport overcell membranes and activation of cell growth. The development of insulinresistance is common both in diabetics and nondiabetics, but it is onlythe glucose transport system that develops resistance to insulin. Tocompensate for the impaired glucose transport, the normal body producesmore insulin and the diabetic patient has to inject higher doses ofinsulin. Since insulin also is a growth hormone, the increased insulinconcentration induces an accelerated growth of atherosclerotic lesionsand increased risk for cardiovascular morbidity and mortality.

The present studies are performed in old, spontaneously hypertensiverats (SHRs), which are known to develop insulin resistance. Racemicamlodipine, (-) amlodipine, and (+) amlodipine are studied for theireffects on glucose transport, insulin plasma concentration and arterialblood pressure.

Prior to receiving vehicle or test compound, basal measurements of thefollowing parameters are made: (1) systolic blood pressure (measured viatail cuff occlusion); (2) fasting levels of plasma insulin andtriglycerides; and (3) glucose tolerance.

The SHRs receive vehicle or test compound via oral gavage once or twicedaily for two or four weeks. Measurements of blood pressure, circulatinginsulin and triglycerides, and glucose clearance are made following two(and four) weeks of drug administration. Any changes in insulinresistance resulting from the drug treatment are evident as changes inthe ratio of plasma glucose/plasma insulin levels and from the glucosetolerance tests.

Example 7 Oral Formulation

Capsules

    ______________________________________                                                    Quantity per capsule in mg.                                       Formula       A          B       C                                            ______________________________________                                        Active ingredient                                                                           0.5        2.5     5.0                                            (-) Amlodipine                                                                Lactose 83.5 81.5 79.0                                                        Corn Starch 15.0 15.0 15.0                                                    Magnesium Stearate 1.0 1.0 1.0                                                Compression Weight 100.0 100.0 100.0                                        ______________________________________                                    

The active ingredient, (-) amlodipine, lactose, and corn starch areblended until uniform; then the magnesium stearate is blended into theresulting powder. The resulting mixture is encapsulated into suitablysized two-piece hard gelatin capsules.

Example 8 Oral Formulation

Tablets

    ______________________________________                                                      Quantity per Tablet in Gm.                                      Formula         A          B       C                                          ______________________________________                                        Active ingredient,                                                                            0.5        2.5     5.0                                          (-) amlodipine                                                                lactose BP 183.0 181.0 178.5                                                  starch BP 15.0 15.0 15.0                                                      Pregelatinized Maize Starch BP                                                magnesium stearate 1.5 1.5 1.5                                                Compression weight 200.0 200.0 200.0                                        ______________________________________                                    

The active ingredient, (-) amlodipine, is sieved through a suitablesieve and blended with lactose, starch, and pregelatinized maize starch.Suitable volumes of purified water are added and the powders aregranulated. After drying, the granules are screened and blended with themagnesium stearate. The granules are then compressed into tablets using7 mm diamter of punches.

Tablets of other strengths may be prepared by altering the ratio ofactive ingredient to lactose or the compression weight and using punchesto suit.

What is claimed is:
 1. A method of eliciting an antihypertensive effectin a human, which comprises administering to a human in need thereof atherapeutically effective amount of (-) amlodipine, or apharmaceutically acceptable salt thereof, substantially free of its (+)stereoisomer, said amount being sufficient to alleviate hypertension. 2.The method of claim 1 wherein (-) amlodipine is administered byintravenous infusion, by transdermal delivery, or orally as a tablet ora capsule.
 3. The method of claim 2 wherein the amount administered isfrom about 0.01 mg to about 100.0 mg daily.
 4. The method of claim 3wherein the amount administered is from about 0.5 mg to about 20 mg. 5.The method of claim 4 wherein the amount administered is from about 0.5mg to about 10.0 mg.
 6. The method of claim 1 wherein the amount of (-)amlodipine or a pharmaceutically acceptable salt thereof is greater thanapproximately 90% by weight of the total amount of amlodipine.
 7. Themethod of claim 1 wherein the amount of (-) amlodipine or apharmaceutically acceptable salt thereof, substantially free of its (+)stereoisomer, is administered together with a pharmaceuticallyacceptable carrier.
 8. The method according to claims 2, 3, 4, 5, or 6,wherein (-) amlodipine is administered as its besylate salt.
 9. A methodof treating angina in a human, which comprises administering to a humanin need thereof a therapeutically effective amount of (-) amlodipine, ora pharmaceutically acceptable salt thereof, substantially free of its(+) stereoisomer, said amount being sufficient to alleviate angina. 10.The method of claim 9 wherein (-) amlodipine is administered byintravenous infusion, by transdermal delivery, or orally as a tablet ora capsule.
 11. The method of claim 10 wherein the amount administered isfrom about 0.01 mg to about 100.0 mg.
 12. The method of claim 11 whereinthe amount administered is from about 0.5 mg to about 20.0 mg.
 13. Themethod of claim 12 wherein the amount administered is from about 0.5 mgto about 10.0 mg.
 14. The method of claim 9 wherein the amount of (-)amlodipine or a pharmaceutically acceptable salt thereof is greater thanapproximately 90% by weight of the total amount of amlodipine.
 15. Themethod of claim 9 wherein the amount of (-) amlodipine or apharmaceutically acceptable salt thereof, substantially free of its (+)stereoisomer, is administered together with a pharmaceuticallyacceptable carrier.
 16. The method according to claims 10, 11, 12, 13 or14 wherein (-) amlodipine besylate is administered.